The present invention relates to a method for operating a restraint system, networked via a bus line, in the event of a short circuit on the bus line, including a central control unit and a plurality of data processing units connected to the bus line, each of the data processing units serving to activate one or more restraint devices.
The capabilities of vehicle restraint systems will increase substantially in the future in order to afford passengers still greater protection. This means that there will be a tremendous increase in the number of restraint devices and associated triggering means installed in vehicles. Examples of such restraint devices are driver and front-passenger airbags, which can be activated in multiple stages, driver and front-passenger knee bags, side airbags for the driver and the front-seat and back-seat passengers, such side airbags optionally being provided for both the head and chest areas, seat-belt pretensioners, which also can be activated in multiple stages, optionally also roll bars, etc. A complex protection system composed of multiple restraint devices for each-passenger will thus be installed in vehicles.
A complex restraint system is described in the German Patent Application No. 47 668.2 and in the Conference Proceedings of the SAE International Congress and Exposition, Feb. 24-27, 1997, Detroit, in the paper xe2x80x9cBussystem zur Vernetzung von Aktuatoren fxc3xcr Rxc3xcckhaltesystemexe2x80x9d [xe2x80x9cBus System for Networking Actuators for Restraint Systemsxe2x80x9d] by J. Bauer, G. Mehler and W. Nitschke. Implementation of a bus system networking all the restraint devices together made it possible to avoid the use of bulky cable harnesses. In this conventional system, provided for each restraint device is a data processing unit, including a processor, data input and output circuits, a memory unit, a time and clock base and a power supply. This data processing unit, also described as a peripheral intelligent driver stage, is located in the immediate vicinity of the triggering device belonging to the respective restraint device, namely, in a firing-pellet connector or a substrate of the firing pellet itself.
Each data processing unit receives its power from a central control unit, via a bus line. In addition, the central control unit determines which restraint devices are to be triggered, on the basis of a plurality of control signals, for example, from acceleration sensors, pre-crash sensors and seat-occupancy sensors. Accordingly, with the aid of a protocol transmitted over the bus line, the central control unit addresses the data processing units concerned. In addition, requests for diagnostic activity are transmitted from the central control unit via the bus line to the individual data processing units, which in turn send their diagnostic responses back to the central control unit via the bus.
As already described in German Patent Application No. 196 47 668.2, failure of the entire restraint system is to be prevented in the event of a short circuit occurring on the bus line, if at all possible. To this end, the central control unit measures short-circuit current on the bus line, and localizes the short circuit by interacting with the data processing units connected to the bus line. This makes it possible for at least all the data processing units located between the central control unit and the short circuit to remain operational, with only those data processing units downstream of the short circuit no longer being accessible to activation by the central control unit. The bus system constructed in this way thus has a certain tolerance for short circuits.
An object of the present invention is to specify a device of the which, as far as possible, maintains the entire restraint system operational in the event of a short circuit on the bus line.
The objective is achieved in that data processing unit in that each data processing unit connected to the bus line measures for short circuits on the bus line. If a short circuit is detected, the data processing unit then starts timing, and opens a circuit breaker contained within it, with which the bus line can be closed or interrupted, if the short circuit measured lasts longer than a preset waiting period.
As all the data processing units used to activate various restraint devices are themselves actively involved in detecting a short circuit, an optimum short-circuit tolerance in the restraint system can be achieved. Namely, the duration of the short circuit is taken into account, such that in the event of a short circuit of only brief duration, the entire restraint system is maintained in an operational state, and in the event of a longer short circuit, at least those data processing units located between the central control unit and the localized short circuit remain active. As a result, a short circuit on the bus line does not inevitably lead to a total failure of the entire restraint system.
The data processing unit can be shifted into a reset state if the duration of the short circuit measured is several times longer than the waiting period after which the circuit breaker is opened.
In practical terms, the central control unit performs a short-circuit measurement on the bus line, starts a time measurement with the commencement of a short circuit, and switches off its power supply to the data processing units connected to the bus line if the short-circuit duration measured by it exceeds a preset hold time. This hold time is shorter than the delay for the opening of the circuit breakers in the data processing units. The central control unit switches the power supply for the data processing units back on again after the latter have opened their circuit breakers. As a result, operation of those data processing units which are disposed between the central control unit and the location of the short circuit can be maintained.
When a triggering command for the restraint devices has to be transmitted after the onset of a short circuit, the central control unit transmits it several times via the bus line, such that after a short circuit of very brief duration, a triggering command will be guaranteed to reach all data processing units concerned.